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Micro-scaled progressive sheet metal forming is a promising process for producing bulk microparts, given its advantages of high efficiency and low cost. To enhance forming quality and efficiency, it is important to have an in-depth understanding of the forming mechanism and model the forming process and fracture behavior accurately. However, the prediction of fracture formation in sheet materials at the micro-scale has not yet been well explored, and thus current knowledge is not sufficient to support the continued development and application of microforming technology. This study investigated progressive sheet forming of magnesium-lithium alloy sheets of different grain sizes to produce bulk microparts directly from sheet metal via shearing, extruding, piercing, and blanking. Using the Gurson–Tvergaard–Needleman (GTN) damage model, the effects of the size factor on the formation and evolution of voids were considered, and the shear-modified GTN model was established by combining Thomason's and Lemaitre's damage mechanics models. The modified model could predict not only the ductile fracture behavior dominated by tension under high-stress triaxiality at the micro-scale, but also the damage behavior controlled by shear deformation under low-stress triaxiality. The progressive forming process was simulated using the modified model, which was verified by experimentation and simulation. Comparisons of the experiments and simulations revealed the size effects on the forming defects and fracture behaviors of microparts during progressive sheet forming. The results show that the stress during deformation is mainly concentrated at the edge of microparts, and irregular geometric defects including burr, rollover, incline, and bulge become deteriorated with the increase of the initial grain size. This study enhances the understanding and prediction of ductile fracture in the micro-scaled progressive forming of sheet metals. [ABSTRACT FROM AUTHOR]

Although researchers have extensively investigated the dynamic mechanical properties of metallic materials at the macro-scale in terms of deformation mechanisms, strain rate strengthening and fracture mechanisms, they have rarely investigated the dynamic mechanical properties affected by size effects at the micro-/meso-scales. In this study, experiments on quasi-static compression and the split-Hopkinson pressure bar (SHPB) were conducted using oxygen-free high-conductivity (OFHC) copper with different geometrical and grain sizes to explore the size effects on various dynamic mechanical properties at the micro-/meso-scales. The experimental results showed that the quasi-static and dynamic mechanical properties of OFHC copper are affected by size effects at the micro-/meso-scales. In particular, OFHC copper was found to exhibit strain rate strengthening effects at the micro-/meso-scales, and the presence of micro-cracks was observed in the SHPB experimental specimens. In this study, after proposing a modified Johnson-Cook (J-C) constitutive model based on the surface layer model, we analysed the average relative error of the modified model and the original constitutive model. The influence of the size effect on the mechanical properties of materials is taken into account in the new modified constitutive model. The results of relative error analysis showed that the average relative errors for the original J-C model ranged from 3.2% to 18%, while the modified J-C model's results ranged from 2.2% to 11%. The accuracy of the modified model is greatly improved. Following finite element analysis based on the modified J-C model and the original model, the results showed that the modified J-C model agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

Micro-forming is one of the major micro-manufacturing methods with promising application potentials, in which the damage response and fracture behavior need to be insightfully addressed. Among all the damage criteria to predict fracture, GTN model is a widely-used one and able to predict void-dominated fracture in micro-scale deformation. However, it is not very applicable under low stress triaxiality and shear-dominated condition. An in-depth understanding of shear damage and its potential size effect are crucial to explore the micro-scaled damage and fracture mechanisms. This research characterizes the size effect on flow stress via employing a combined constitutive model, and an approach for applying a phenomenological shear damage evolution law to the GTN-Thomason model via considering the size effect is developed. The prediction of micro-scaled fracture in a wide stress triaxiality range is thus enabled. Through simulation and experiment, the proposed model is validated and verified. In addition, stress state parameters including stress triaxiality, Lode parameter, and weight function, are also discussed, and the two damage parameters are analyzed quantificationally to reveal different fracture mechanisms occurring in different stress states and grain sizes. The research thus facilitates the physical insight and in-depth understanding of the size effect on damage evolution and fracture formation in micro-scaled plastic deformation of materials. Unlabelled Image • A new micro-scaled model is proposed for fracture under low stress triaxiality. • Shear damage and its size effect is considered in a phenomenological way. • Void and shear damage can be quantified by two independent parameters. • With the increase of grain size, fracture becomes more shear-dominated. [ABSTRACT FROM AUTHOR]

The development of flexible electronics has placed higher demands on electromagnetic interference (EMI) shielding materials, especially in terms of mechanical properties. Herein, a novel composite with excellent mechanical and EMI shielding properties was developed. The electrohydrodynamic atomization deposition approach was used to deposit Ti 3 C 2 T x MXene and graphene oxide (GO) nanosheets on carbon fiber fabric (CFf) surface, then they were assembled layer by layer with thermoplastic polyurethane (TPU) and thermoformed at high temperature to obtain MG/f-CFf/TPU composite. When the MXene/GO content increases, the mechanical performance of the composite is improved, mainly owing to the formation of chemical bonds and the presence of mechanical interlocking and van der Waals forces. Specifically, the tensile strength and interlaminar shear strength of the composite reach 140.98 MPa and 54.67 MPa, increasing by 72.45 % and 52.92 %, respectively. Benefitting from the unique lamellar structure, the maximum EMI-SE of MG/f-CFf/TPU composite is 38.29 dB. Besides, the MG/f-CFf/TPU composite also displays outstanding EMI-SE stability after 3000 times folding cycles. The flexible MG/f-CFf/TPU composite may provide more guidelines for the design of next-generation flexible EMI shielding materials. [Display omitted] • The mechanical and EMI shielding properties are improved by adding MXene/GO hybrids. • The tensile strength and ILSS of the composite are 140.98 MPa and 54.67 MPa, respectively. • The composite shows a superior EMI shielding effectiveness of 38.29 dB. • The composite displays outstanding flexibility and EMI-SE stability. [ABSTRACT FROM AUTHOR]

Laser shock clinching is a novel joining method derived from laser shock forming in which the metal foil is plastically deformed under the pulsed laser induced shock wave, and then two or more metal foils can be joined together based on plastic deformation. However, the present researches are less concerned with the mechanical joining behavior of metal foils during incremental impacts of multiple laser pulses. In the present study, the mechanical joining behavior of pure copper foil and pre-pierced stainless steel sheet in laser shock clinching was investigated. A finite element model was established to analyze the material flowing and clinching behavior of metal foils under multiple laser pulses. Based on the validated model, the deformation stages, thickness change, and shock wave propagation features were studied. The temperature rise during clinching was assessed considering both the compression by shock wave and plastic deformation at high strain rates. It is revealed that the laser shock clinching process can be divided into three deformation stages, that is, free bulging forming, radial expansion, and formation of interlock. Both experimental and numerical results prove that the formation of clinched joints relies on the plastic deformation of the joining partner I. The thinnest region of the joint locates at the material of the joining partner I in contact with the upper corner of the joining partner II. In addition, there is no obvious influence of temperature increase on the mechanical properties of joining partners. Moreover, the shock wave propagation characteristics along axial direction and the influence of laser power density on interlock value and thickness distribution were also discussed. [ABSTRACT FROM AUTHOR]

Electromagnetic shielding materials play a significant role in solving the increasing environmental problem of electromagnetic pollutions. The commonly used metal‐based electromagnetic materials suffer from high density, poor corrosion resistance, and high processing cost. Polymer composites exhibit unique combined properties of lightweight, good shock absorption, and corrosion resistance. In this study, a novel high angle sensitive composite is fabricated by combining carbon fiber (CF) fabric with thermoplastic polyurethane elastomer (TPU). The effect of stacking angle of CF fabric on EMI shielding performance of composite is studied. When the stacking angle of CF fabric changed, the electromagnetic interference (EMI) shielding effectiveness (SE) of CF fabric/TPU composite can reach a maximum of 73 dB, and the tensile strength can reach 168 MPa. In addition, the composite has anisotropic conductivity, which is conductive along the plane direction and nonconductive along the thickness direction. Moreover, the CF fabric/TPU composite manifests exceptional EMI‐SE/density/thickness value of 383 dB cm2 g−1, which is higher than most of current EMI shielding composites reported in literature. In summary, CF fabric/TPU composite is an excellent EMI shielding material that is lightweight, highly flexible, and mechanically robust, which can be applied to the field of aerospace and some intelligent electronic devices. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cells have been used worldwide due to their high energy density and zero emissions. The metallic bipolar plate is the crucial component and has a significant effect on a cell's efficiency. However, the springback behavior of the metallic bipolar plate will greatly influence its forming accuracy in the micro-scale sheet metal forming process. Therefore, accurate calculation of the springback angle of the micro-scale metallic bipolar plate is urgent but difficult given the state of existing elastoplastic theory. In this paper, a constitutive model that simultaneously considers grain size effect and strain gradient is proposed to analyze micro-scale bending behavior and calculate springback angles. The specialized micro-scale four-point bending tool was designed to better calculate the springback angle and simplify the calculation step. A pure micro-bending experiment on a 316LN stainless steel sheet with a thickness of 0.1 mm was conducted to verify the constitutive model's accuracy. [ABSTRACT FROM AUTHOR]

The forming defects at elevated temperature caused by the microstructural evolution such as grain size, crystal orientations are the critical issue that induced deformation inhomogeneity and local damage which severely limits the application of Al-Zn-Mg alloys in thin-walled structure manufacturing. In this study, the hot deformation behavior and microstructural evolution were investigated via hot stretching tests, electron backscatter diffraction (EBSD) and the transmission electron microscopy (TEM) characterization. Then, an integrated multiscale constitutive model coupled dislocation density based crystal plasticity (CP) model and phase field method (PFM) was established through the reconstructed configuration of deformation gradient emphasized on a damaged part. The coupled CP-PFM model was numerically implemented into Düsseldorf Advanced Material Simulation Kit (DAMASK) software. Subsequently, a set of virtual polycrystalline RVE models assigned with different average grain sizes and two types of RVE models with realistic crystal orientations were constructed from EBSD data. The experimental and simulation results of the Al-Zn-Mg alloy under hot tensile loading showed that the grain size refinement leads to the increase of grain boundary density, which leads to the rapid increase of dislocation density, uniform damage distribution and better work hardening ability. In addition, the coordination of the activation of different slip systems between adjacent grains will lead to the uneven distribution of dislocation density and local damage. [Display omitted] • An integrated crystal plasticity and phase-field anisotropic damage model is newly established. • Fracture mechanisms are revealed by recrystallization induced grain refinement. • Grain size and orientations affects grain boundaries density, and further dominates deformation inhomogeneity. • The damage is more likely to occur between grains with smaller Schmid factor. [ABSTRACT FROM AUTHOR]

• MWCNTs deposition can give aramid fibers conductivity. • PDA makes MWCNT easier and more effective to deposit on the aramid fiber. • The addition of MWCNTs increases the average phase modulus of the composite. With wearable smart textiles playing an increasingly important role in people's life, aramid fiber (AF) stands out among high-performance materials due to its outstanding flexibility, high strength, and impact resistance. However, its excellent insulation makes it unable to sense and respond to external stimuli, which seems to be a call to multiwalled carbon nanotubes (MWCNTs) with high conductivity. In this paper, the effect of MWCNTs in enhancing the electrical properties and interfacial strength of aramid fiber reinforced polymer (AFRP) composites was researched. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) proved that the polydopamine (PDA) layer and MWCNTs were successfully grafted onto the surface of the AF. Scanning electron microscopy (SEM) showed that the distribution of MWCNTs on the fiber surface is quite uniform and dense. As a result, the adhesion of PDA is more conducive to the deposition of MWCNTs, compared with the pristine aramid fiber. The modified fiber AF-PDA-MWCNTs obtained a resistance on the order of 104 MΩ without reducing its mechanical properties (the tensile strength has obtained an increase of 10.59%). The composite material may also have good interface properties, with the interlaminar fracture toughness G I increased by 200.99%. After being endowed with electrical properties, aramid fibers have strong potential in wearable textiles due to their flexibility, high sensitivity to various deformations, and excellent safety protection performance. [ABSTRACT FROM AUTHOR]

Ultra-high performance flexible superhydrophobic surfaces have attracted great research interests, which are widely used in anti-fog, anti-icing, anti-fouling, self-cleaning, and other fields. However, ultra-high hydrophobic properties and complex manufacturing processes are still huge challenges to be solved. In this paper, a facile construction strategy of ultra-high performance flexible and controllable superhydrophobic films was proposed, combining the template transfer and electrospinning methods. The effects of electrospinning parameters on the microstructure and surface wettability were systematically studied, and the controllable preparation of films with different wettability was realized. Under the stable Cassie-Baxter state, the contact angle of prepared superhydrophobic films could reach 172° and the sliding angle could reach 3°. In addition, the stretchability, abrasion resistance, and chemical durability tests were also conducted in simulated harsh real-world environments. The results indicated that the films still exhibited superior performances. For the practical demonstration, the films are expected to be used as protective films for windshields, outdoor electronic screens, and solar cells due to the inherent optical properties and excellent fouling resistance performance. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The composite was prepared by electrohydrodynamic atomization deposition, layer-by-layer stacking and hot pressing technology. • The synergistic strengthening effect of van der Waals forces and covalent bonds improved the tensile strength of the composite. • The composite showed outstanding resistance stability, flexibility and electromagnetic interference shielding stability. It is a challenge to design Ti 3 C 2 T x MXene-based electromagnetic interference (EMI) shielding composites with excellent mechanical properties. Herein, a highly robust, flexible and durable Ti 3 C 2 T x MXene/carbon fiber fabric/thermoplastic polyurethanes (Ti 3 C 2 T x MXene/CFf/TPU) composite was fabricated through simple electrohydrodynamic atomization deposition, layer-by-layer stacking and hot pressing technology. The synergistic strengthening effect of van der Waals forces and covalent bonds can improve the tensile strength of the composite up to170.2 MPa, which is far greater than that of other MXene-based composites previously reported. In addition, the EMI shielding performance of the Ti 3 C 2 T x MXene/CFf/TPU composite also improved with increasing MXene mass fraction, reaching 40.4 dB, which can be attributed to the dielectric loss provided by conductive fillers and the enhanced absorption within the sandwich structure. More interestingly, the composite retained excellent resistance stability, EMI-SE stability and flexibility, even after multiple bending and releasing cycles. This work provides a facile and environmentally-friendly method for preparing composites with excellent EMI shielding properties and mechanical properties, which may provide more possibilities for applications in intelligent wear and electronic wireless communication equipment. [ABSTRACT FROM AUTHOR]